Color television picture tube of the single electron gun type

ABSTRACT

A color television picture tube of the single electron gun type includes an electron gun composed of a cathode for emitting electrons, control grids disposed in the neighborhood of said cathode, a first anode, and a set of electrodes constituting an electron lens for converging the electron beams emitted from said cathode. A plurality of phosphor dots of different colors are formed on the face of the tube. A shadow mask is disposed between said phosphor dots and said electron gun. An electron beam image is formed in the interior of said electron lens. Voltages on each electrode focuses the crossover point of the electron beams on the surface of said shadow-mask. By postdeflection focusing the beam at the shadow-mask is focused on said phosphor dots in positions corresponding to a plurality of portions of said electron beam.

I United States Patent i 13,558,968

[72] Inventor Kenjiro Takayanagi 2,685,660 8/1954 Norgaard 315/2l(UX) Kamakura, Japan 3,444,421 5/1969 Shimada et a1. 315/21 [21] P 743506 Primary Examiner-Rodney D. Bennett, Jr. [22] Flled July 1968 Assistant Examiner-Brian L. Ribando [45] Patented Jan. 26, 1971 Attome Berna [73] Assignee Victor Company of Japan, Limited y Kanagawa-ku Yokohama City, Japan [32] Priority July 13, 1967 [33] Japan [31] 42/44,871

ABSTRACT: A color television picture tube of the single elec- [54] COLOR TELEVISION PICTURE TUBE OF THE tron gun type includes an electron gun composed of a cathode SINGLE ELECTRON GUN TYPE for emitting electrons, control grids disposed in the neighbor- 8 Claims Drawing Figs hoodof said cathode, a first anode, and a set of electrodes 7 constituting an electron lens for converging the electron [52] U.S. CI 315/13, beams i d f id athode. A plurality of phosphor dots 313/69 of different colors are formed on the face of the tube. A [51] Int. Cl H0lj 29/46 h d k i di osed between said phosphor dots and said [50] Field of Search 315/21, electron gun. An electron beam image is f d i the interior 13CCT 313/69 of said electron lens. Voltages on each electrode focuses the References Cited crossover point of the electron beams on the surface of said shadow-mask. By postdeflection focusing the beam at the UNITED STATES PATENTS shadow-mask is focused on said phosphor dots in positions 2,672,575 3/1954 Werentels 315/21 corresponding to a plurality of portions of said electron beam.

2 I 15 I 15 I6 43 20 i T; 14 1.; F l c a -l- ..:.r,. t, I a? l] L L 3, pin ftr/a/v (o/A =5 t 4 PATENTED M26197: 3,558,968

SHEET 2 OF 3 INVENTOR Kammo Rmvamwn ATTORNEY PATENTEHJANZSIBYI 3558.968

SHEET 3 OF 3 INVENTOR KENJIRD THKHYHNHG-I ATTORNEY COLOR TELEVISION PICTURE TUBE OF THE SINGLE ELECTRON GUN TYPE DISCLOSURE This invention relates to color television picture tubes, and more particularly to color television tubes of the postdeflection focusing type having a single electron gun.

The most generally used color television picture tube is the so-called three gun, shadow-mask, color picture tube, which was developed by the Radio Corporation of America. This tube includes three electron guns, each disposed on an in dividually associated corner of an equilateral triangle.

Several problems are encountered in this type three gun of picture tube. Since the three electron guns are mounted independently of one another, the spacing between the electron beams emitted fromthe electron guns is limited by the diameter of electrodes of the three electron guns. It is thus impossible to reduce the spacing below a given level. This makes it necessary to adjust static and dynamic convergences so that each of the three electron beams may be accurately positioned to strike the phosphor dots, as desired and so that the three beams may simultaneously pass through the same aperture in the shadow-mask. The picture tube must have a complicated construction if such adjustments are to be effected. The method of making these adjustments is also complicated and requires a considerable skill. Moreover, the performance of the picture tube lacks stability.

The shadow-mask used with this type of picture tube has apertures of a relatively small diameter. The ratio of the electron beams passing through the apertures to those that fail to pass therethrough has a low value of about percent. As a result, the brightness of the color picture is lower than the brightness of a comparable black-and-white picture tube. An attempt to increase the brightness of the picture is inevitably accompanied by a marked lowering of resolution due to blooming because a large amount of the electron beams must flow.

The chromatron tube reported by Prof. Lawrence has an arrangement of electrodes which makes a single electron gun of the postdeflection focusing type. The phosphor screens of this type of picture tube are coated with colored phosphors of red, green, blue and green colors arranged in a linear pattern in the indicated order. A pair of grille electrodes are mounted in a position spaced apart from the phosphor screens toward the electron gun. Each of these electrodes includes a number of thin multifilament which are metal wires electrically insulated from one another. An alternating voltage is applied between these grille electrodes so that a single electron beam can scan the phosphors of different colors in chronological sequence.

In this type of picture tube, the alternating voltage must have a high frequency (for example, the subcarrier frequency of a color video signal is 3.58 maga hertz) in order to prevent the occurrence of color flicker in the colored image displayed on the screen. This results in an increase of reactive power due to the electrostatic capacity between the grille electrodes. This also makes it necessary to increase the output of a generator of this alternating voltage. Accordingly, this arrangement causes an increase in the cost of forming the circuit. In addition, this picture tube has a disadvantage in that the voltage of the generator is induced in the other circuits, and that induced voltage, in turn, causes failures.

The present invention overcomes the aforementioned disadvantages of prior art color television picture tubes. According to the invention, the single electron gun is composed of a cathode. Three control grids are disposed in the neighborhood of the cathode. Each grid is formed as one of three equal parts obtained by dividing a ring, of a small thickness, in the portion of the grids facing toward the electron-emitting surface of the cathode. A first anode and a set of cylindrical electrodes constitute an electron lens for causing the electron beam emitted from the cathode to converge. The shadow-mask electrode is also used as a converging electrode so that postdeflection focusing can be effected.

The density of the electron beam emitted from portions of the cathode which are in face to face relationship with the control grids is controlled by the voltage on the respective control grids. If primary color signals representing three primary colors are applied to the corresponding control grids and if the electron beam image is formed on the phosphor screen, one electron beam strikes the phosphor screen which consists of three components. Each component then has an electron density corresponding to each primary color signal voltage. Therefore, if the phosphor dots of three primary colors are arranged in positions corresponding to the three components, a color television signal is reproduced as a colored image on the television screen.

Since there is one electron beam for three primary colors, there is no need for making adjustments of static and dynamic convergences for three guns spaced apart from one another. This results in a simplification of the construction of the picture tube, an easy adjustment of the mechanism, and an elimination of a voltage regulator for maintaining a constant voltage on the phosphor screen. It is thus possible to use a simple deflection device which is substantially similar to the device used with a black-and-white television picture tube. Moreover, the use of a postdeflection focusing system facilitates deflection of the electron beam and enables a brighter picture image because the apertures of the shadowmask can have a larger diameter.

Accordingly, the principal object of this invention is to provide a color television picture tube for a color television receiving set which can give a reliable performance and which can be produced at a cost substantially similar to that of a black-and-white television receiving set.

Another object of the invention is to provide a color television picture tube which uses a simple electron beam deflection device substantially similar to that used with a black-andwhite television picture tube.

Still another object of the invention is to provide a color television picture tube which eliminates the requirement for adjustments of static and dynamic convergences.

A further object of the invention is to provide a color television picture tube which produces a bright image on the television screen.

Other objects and advantages of the invention will become apparent from consideration of the following description when taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic view showing an arrangement of electrodes in one embodiment of the color television picture tube according to this invention;

FIG. 2 is a circuit diagram, shown partly in a block diagram, for applying voltages and signals to the electrodes shown in FIG. 1;

FIGS. 3A and 3B are schematic views for explaining the manner in which the electron beam is converged in an electron gun composed of some of the electrodes shown in FIG. 1;

FIG. 4 is an enlarged schematic front view of control grids embodying this invention;

FIG. 5 is a schematic view showing an electron density image of the electron beam formed in an electron lens;

FIG. 6A is a schematic view showing the manner of travel of the electron beam resulting from an application of equal voltages to the three control grids shown in FIG. 4;

FIG. 6B is a schematic view showing the manner of travel of the electron beam resulting from an application of a voltage to a specific one of the three control grids shown in FIG. 4, with a cutoff voltage being applied to the remainder of the control grids;

FIG. 7 is a schematic view in explanation of the manner in which the electron beam is converged by the electric field created between the phosphor screen and the shadow-mask;

FIG. 8 is a schematic view showing the shape and arrangement of phosphor dots forming a phosphor screen; and

FIG. 9 is'a schematic view in explanation of the manner in which the electron image of the electron beam of FIG. 5 is formed on the phosphor screen.

The external shape of a color television picture tube embodying this invention is substantially similar to that of the conventional shadow-mask color television picture tube, so that its illustration is omitted. However, essential portions of the inventive color television picture tube are shown in FIG. 1. A phosphor screen 12 is composed of phosphor dots which are deposited on the inner side of a transparent face plate 11 and housed in an evacuated glass bulb. A metal back 13, consisting of aluminum, is applied to the surface of the phosphor screen 12 by sputtering. Also housed in the evacuated glass bulb are a cathode 14, a control grids 15 of special shape, a first anode 16, and a cascaded series of cylindrical electrodes 17, 18, and 19. Taken together, the elements 14-19 constitute an electron-gun. A shadow-mask is disposed in the neighborhood of the phosphor screen 12. Horizontal and vertical deflection coil 21 provides a means for deflecting the electron beam emitted from said electron gun,

It is to be observed that the arrangement of electrodes in the color television picture tube embodying this invention is substantially similar to that of a conventional black-and-white television picture tube except for the shadow-mask 20 and the special shape of the control grids 15.

Means are shown in FIG. 2 for applying voltages and signals to the aforementioned electrodes so that the picture tube may operate as a color television picture tube. A high positive voltage is applied from a high voltage generator (not shown) through a terminal 22 to the phosphor screen 12. This same generator is also connected fromterminal 22 to the ground of a television receiving set through a series bleeder circuit composed ofa resistor 23, variable resistor 24, resistor 25, variable resistor 26, variable resistor 27 and a variable resistor 28. The shadow-mask 20 is connected to an adjustable contact 29 of the variable resistor 24. The electrodes 17 and 19 are electrically connected to each other in the interior of the glass bulb, and their junction point is connected to the junction point between the variable resistor 24 and resistor 25. The electrode 18 is connected to an adjustable contact 30 of the variable resistor 26. The first anode 16 is connected to an adjustable contact 31 of the variable resistor 27. The control grids 15 are connected to an adjustable contact 33 of the variable resistor 28 through a resistor 32. The cathode 14 is connected to the junction point between the variable resistors 27 and 28 through a resistor 34.

The brightness signal of a color television signal is applied to the cathode 14 by a video amplifier 35. The red-yellow (R-Y) color difference signal is applied to the control grids 15 by a matrix circuit 36. Though only the (R-Y) color difference signal is shown as being applied, it is to be understood that the green-yellow (GY) and blue-yellow (B-Y) color difference signals are applied in addition to the (R-Y) signal. It is also to be understood that the resistors 32 and 34 as well as the variable resistors and resistors making up a bleeder circuit as aforementioned are disposed outside of the glass bulb of the color television picture tube.

A saw tooth wave current is fed to the deflection coil 21 from a vertical and horizontal deflection circuit 46 so that the electron beam emitted from the electron gun may be deflected to make the raster on the phosphor screen 12.

The electron beams as it is emitted from the electron gun when voltages and signals are applied to the aforementioned electrodes will now be described with reference to FIGS. 3- 9.

FIG. 4 schematically shows the control grids 15, according to this invention, as seen from the phosphor screen 12. As shown, the control grids 15 include three electrodes spaced an equidistance apart to provide a red color grid l5r, a green color grid 15g, and a blue color grid 15b. Each of these grids is shaped and disposed, on a single surface of the side facing toward the electron emitting surface of the cathode 14, in such a manner that together they constitute three equal parts of a metal ring separated from one another by gaps 37, 38, and 39. The grids l5r, 15g, and 15b possess terminals 40r, 40g and 40b respectively. The electron beam emitted from the cathode 14 passes through an opening 41 formed by the grids l5r, 15g and 15b.

Let us assume that the color difference signals (R-Y), (G- Y) and (B-Y) are equal in value. The matrix circuit 36 applies the color difference signal (R-Y) to the red color control grid l5r through the terminal 40r, the color difference signal (G- Y) to the green color control grid 15g through the terminal 40g, and the color difference signal (B-Y) to the blue color control grid 15b through the terminal 40b. A Y-signal is applied by the video amplifier 36 to the cathode 14. To focus an image, the potential of the first anode 16 is adjusted by moving the adjustable contact 31 of the variable resistor 27. An electron density image e on the electron emitting surface of the cathode 14 is transmitted through a crossover point 42 and focused on a plane substantially in the center of the electron lens composed on the electrodes 17, 18 and 19. This forms an inverted image e" on the plane owing to the electron lens action of the electric field created between the first anode 16 and the electrode 17. FIG. 3B explains the formation of this inverted image from the optical point of view.

The electron density image 2 formed on the electron emitting surface of the cathode 14 is made up of a portion e'r controlled by the voltage applied to the red color control grid l5r, a portion e controlled by the voltage applied to the green color control grid 15g, and a portion e'b controlled by the voltage applied to the blue color control grid 15b. The inverted image e" focused in the electron lens would, if enlarged, be found to be composed of three segmental dots Dr, Dg and Db as shown in FIG. 5. The manner of travel of the electron beam 43 in the neighborhood of the first anode 16 is shown in detail in FIG. 6A.

If the color difference signal (R-Y) is applied to the red color control grid l5r, while maintaining the potential of the rest of the control grids below the cutoff level, the electron density image e on the electron emitting surface would only have the portion e',. The electron beam 43 would travel in a manner shown in FIG. 6B, and the inverted image ewould consist of only one segmental dot Dr. Similarly, if the color difference signal (G-Y) is applied to the green color control grid 15g, while maintaining the potential of the other control grids l5r and 15b below the cutofflevel, the inverted image e" would consists of only one segmental dot Dg. If the color difference signal (B-Y) is applied to the blue color control grid 15b, while maintaining the other control grids l5r and 15g below the cutoff level, the inverted image 2" would consist of only one segmental dot Db.

The size of the segmental dots Dr, Dg and Db may vary depending on the value of voltages applied to the control grids l5r, 15g and 15b which control the dimension of each segment.

It is possible to form the inverted image e" upon the three segmental dots Dr, Dg and Db whose size can be controlled. It would be possible to obtain a colored image on the television screen by causing the inverted image e to be formed through another electron lens. That other lens would focus the image on the phosphor screen 12 on which are deposited circular phosphor dot assemblies 44 (FIG. 8). Each dot consists of a red colored phosphor dot R, a green colored phosphor dot G, and a blue colored phosphor dot B disposed in positions corresponding to the segmental dots Dr, Dg and Db of the inverted image 2 formed on the phosphor screen.

Means are provided for causing the inverted image e" to be formed on the phosphor screen 12.

Referring to FIGS. 1 and 2, the adjustable contact 30 of the variable resistor 26 is moved to adjust the voltage applied to the cylindrical electrode 18 so as to control the focal length of the electron lens formed by the electric field created in the cylindrical electrodes 17, 18 and 19. This causes the electron image in the crossover point of the electron beam 43 emitted from the cathode to be formed on the shadow-mask. The electron beam 43 focused on the shadow-mask has the smallest possible cross-sectional area corresponding to that of the crossover point 42. This enables an increase in the ratio of the electrons in the beams passing through the apertures of the shadow-mask to the electrons in the beams prevented from passing therethrough. Accordingly, a large quantity of electrons can be made to strike the phosphor screen, thus increasing the brightness of a colored image on the television screen.

A known postdeflection focusing operation causes the inverted image 2'', formed in substantially the center of the cylindrical electrode 18 (See FIG. 3), to come to a focus on the phosphor screen 12. The adjustable contact 29 of the variable resistor 24 is moved to select the resistance value wherein the difference in potential (Ep) between the phosphor screen 12 and the shadow-mask and the potential (E0) of the shadow-mask 20 satisfy the following relation:

This voltage relationship forms an electron lens in an electric field in portions of the shadow-mask corresponding to apertures 45 (FIG. 7). The electron lens focuses the inverted image e" on the phosphor screen 12. The red colored phosphor dot R, green colored phosphor dot G, and blue colored phosphor dot B are excited respectively by the sector dots Dr, Dg, and Db constituting the inverted image e and disposed in positions corresponding to the positions of the three colored phosphor dots respectively. Thus, the phosphor dots are caused to emit light and consequently a colored image can be formed on the phosphor screen. FIG. 9 shows, by an optical equivalent, the aforementioned convergence of the electron beam. FIG. 7 shows the manner in which convergence of the electron beam is effected in a postdeflection operation.

As described above in detail, the color television picture tube embodying this invention has one gun including three control grids, one cathode, and one set of cylindrical electrodes making up an electron lens. The electron beam emitted from this electron gun consists of a plurality of components, each having an electron density which varies depending on the amplitude of a respective primary color signal. The electron beam functions as a single electron beam when considered as a unit so that the color television picture tube of this invention can achieve excellent results as described in the opening paragraphs of this specification. Moreover, the color television picture tube embodying this invention has additional features which are set forth hereunder.

The provision of only one electron gun, as contrasted to three electron guns of the convention color television picture tube, enables a reduction of both the diameter of a glass envelope for housing the electron gun and the diameter of the neck of the picture tube. This increases a deflection sensitivity of the deflection coil. If the inventive picture tube has a neck of the same diameter as the neck of a conventional picture tube, the diameter of the cylindrical electrodes making up an electron lens can be increased to provide a large aperture electron lens. This is conducive to a minimization of astigmatism and coma of the lens system. The well-defined electron beam spots has sharp edges which are projected onto the phosphor screen. As a result, the inventive tube can produce a clear colored image on the screen which is of high resolution and free from color contamination.

The present invention has been described as being embodied in a color television picture tube of the three color type. However, it is to be understood that the invention is not limited to the precise form of the embodiment described. The invention can be embodied in color television picture tubes of two color type or more than three colors. Other changes and modifications which are obvious to persons skilled in the art can also be made in the embodiment without departing from the scope and spirit of the invention.

lclaim:

l. A color picture tube comprising a single electron gun including a cathode beam-emitting electrode, a plurality of control grids, a first anode, and a cascaded series of cylindrical electrodes, means comprising a phosphorescent screen of colored dots positioned in the path of electrons emanating from said electron gun, an apertured shadow-mask interposed between said gun and said phosphorescent screen, means for controlling the voltage applied to said first anode for focusing an image of said electron beam inside said cylindrical electrodes, means for controlling the voltages applied to said cylindrical electrodes for focusing said beam on said shadow mask, means for controlling the voltage applied to said shadow-mask to cause said image to be reformed as a single spot on said phosphorescent screen, and means for applying the single spot of said reformed image to said colored dots'in accordance with the original colors of said picture.

2. The picture tube of claim 1 wherein said cylindrical electrodes focus said electron beam to have a crossover focal point at said shadow-mask.

3. The picture tube of claim 1 wherein said control grids include a plurality of electrodes disposed in the same plane and positioned equidistant from each other, said electron beam passing between said grids, and means for applying color signal voltages to said grids to deflect said electron beam to corresponding colored dots.

4. The picture tube of claim 1 wherein said cathode beamemitting electrode has an electron image of first electron density, said image inside said cylindrical electrodes has a second electron density, and said reformed image has a third electron density.

5. The picture tube of claim 3 wherein said cathode beamemitting electrode has a first electron image with a plurality of portions corresponding to picture colors, said phosphorescent dots having a corresponding plurality of portions with each portion having a color corresponding to a portion of said image on said beam emitting surface.

6. The picture tube as claimed in claim 5 in which said control grids include three electrodes each having a side facing the electron-emitting surface of said cathode, said sides being shaped to provide three equal parts of a metal ring formed of a conducting material, said parts being separated from each other by gaps in said ring, said plurality of portions of said first electron image being shaped as segments formed by dividing a circle into three equal parts, said phosphor dots also being shaped as segments formed by dividing a circle into three equal parts, and said phosphor screen has circular phosphor spots, each spot being composed of said phosphor dots of different colors.

7. The picture tube as claimed in claim 6 in which said color signal voltages are color difference signals ofa color television signal, and means are provided for applying a brightness color television signal to said cathode.

8. A color television picture tube as claimed in claim 1 in which said cascaded series of cylindrical electrodes includes three coaxially mounted cylindrical electrodes, and means for causing a crossover focal point of the electron beam to come to a focus on said shadow-mask, said last named means comprising means for controlling the voltage applied to the intermediate cylindrical electrode of said three cylindrical electrodes. 

1. A color picture tube comprising a single electron gun including a cathode beam-emitting electrode, a plurality of control grids, a first anode, and a cascaded series of cylindrical electrodes, means comprising a phosphorescent screen of colored dots positioned in the path of electrons emanating from said electron gun, an apertured shadow-mask interposed between said gun and said phosphorescent screen, means for controlling the voltage applied to said first anode for focusing an image of said electron beam inside said cylindrical electrodes, means for controlling the voltages applied to said cylindrical electrodes for focusing said beam on said shadowmask, means for controlling the voltage applied to said shadowmask to cause said image to be reformed as a single spot on said phosphorescent screen, and means for applying the single spot of said reformed image to said colored dots in accordance with the original colors of said picture.
 2. The picture tube of claim 1 wherein said cylindrical electrodes focus said electron beam to have a crossover focal point at said shadow-mask.
 3. The picture tube of claim 1 wherein said control grids include a plurality of electrodes disposed in the same plane and positioned equidistant from each other, said electron beam passing between said grids, and means for applying color signal voltages to said grids to Deflect said electron beam to corresponding colored dots.
 4. The picture tube of claim 1 wherein said cathode beam-emitting electrode has an electron image of first electron density, said image inside said cylindrical electrodes has a second electron density, and said reformed image has a third electron density.
 5. The picture tube of claim 3 wherein said cathode beam-emitting electrode has a first electron image with a plurality of portions corresponding to picture colors, said phosphorescent dots having a corresponding plurality of portions with each portion having a color corresponding to a portion of said image on said beam emitting surface.
 6. The picture tube as claimed in claim 5 in which said control grids include three electrodes each having a side facing the electron-emitting surface of said cathode, said sides being shaped to provide three equal parts of a metal ring formed of a conducting material, said parts being separated from each other by gaps in said ring, said plurality of portions of said first electron image being shaped as segments formed by dividing a circle into three equal parts, said phosphor dots also being shaped as segments formed by dividing a circle into three equal parts, and said phosphor screen has circular phosphor spots, each spot being composed of said phosphor dots of different colors.
 7. The picture tube as claimed in claim 6 in which said color signal voltages are color difference signals of a color television signal, and means are provided for applying a brightness color television signal to said cathode.
 8. A color television picture tube as claimed in claim 1 in which said cascaded series of cylindrical electrodes includes three coaxially mounted cylindrical electrodes, and means for causing a crossover focal point of the electron beam to come to a focus on said shadow-mask, said last named means comprising means for controlling the voltage applied to the intermediate cylindrical electrode of said three cylindrical electrodes. 